lustre: switch to kernel_sendmsg()

(casts are due to misannotations in lustre; it uses iovec where kvec would be
correct type; too much noise to properly annotate right now).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc drivers/staging/lustre/lnet/klnds/socklnd/socklnd_lib-linux.c
Simple merge

diff --cc drivers/staging/lustre/lustre/libcfs/linux/linux-tcpip.c
Simple merge